Before the exam he was so nervous he looked spaced out.
Tips
usage
Describes a visible mental state — you look out of it. Often follows 地 as an adverbial (神情恍惚地 + verb) or follows 显得/看起来. Different from 心不在焉 (heart-not-here) which stresses inattention more than the dazed look.
memory
恍惚 on its own already means 'dazed / in a trance.' 神情 ('expression') adds 'and you can see it on their face.'
